1. Field of the Invention
The present invention is generally related to a breakaway skeg and, more particularly, to a system for attaching a skeg to a housing structure in a manner that causes attachment points to sequentially disengage so that the moment caused by an impact force needed to separate the skeg from the housing structure can be accurately preselected.
2. Description of the Related Art
Those skilled in the art of marine propulsion devices are familiar with many types of attachment techniques that are intended to be used in conjunction with skegs. Some attachments are intended to provide desirable maneuvering capability while others are intended to physically protect the skeg from damage. Other techniques are known for the purpose of allowing a skeg to breakaway, in a sacrificial manner, in order to protect the marine propulsion device from more serious damage.
U.S. Pat. No. 4,995,840, which issued to Seale et al. on Feb. 26, 1991, describes a stabilizing fin for a motorboat. It is provided with a thickened trailing edge in order to act as a flap for inducing drag during startup. The induced drag serves to minimize the time within which the fin moves into a planing position. The recess on the bottom surface of the fin enhances the lifting force on the fin during stabilization without imposing undue drag forces during high speed travel of a boat.
U.S. Pat. No. 5,007,868, which issued to Fry on Apr. 16, 1991, describes a replaceable skeg for a marine propulsion device. It includes a tapered dovetail tongue and groove joint between top of the skeg and lower portion of a gear case housing on the marine propulsion device. When the skeg is hit by an underwater obstruction it will fracture at the joint and break away, leaving the lower portion of the gear case housing in tact and undamaged in which another skeg can be installed thereto.
U.S. Pat. No. 5,007,869, which issued to Zoellner on Apr. 16, 1991, describes a propeller guard device. It includes a laterally extending fin and a vertical extension or sleeve. The fin and sleeve could be manufactured as a single item. The vertical sleeve is attached to the midline area of the fin with the leading edge of the sleeve being generally coterminous with the leading edge of the fin. The fin is at least as wide as the rotational path of the propeller blades. The singular fin extends laterally on either side of the sleeve in a generally coplanar relationship. The leading edge of the fin is elevated from three to five degrees higher than the trailing edge of the fin. The trailing edge of the fin is located forwardly of the rotational path of the propeller blades or is lengthened and extends towards the rear of the device to the extent of being even with the midline of the rotational path of the propeller blades.
U.S. Pat. No. 5,018,997, which issued to Guptill on May 28, 1991, describes a skeg protector. It is mounted on the leading edge of the skeg of a boat motor. The protector is in the form of a channel of stainless steel fitted on the skeg with the base of the channel spaced forwardly of the leading edge of the skeg. A rubber strip extends along the inside of the channel. To mount the protector on the skeg, elongate, horizontal slots are formed in the channel flanges and holes are drilled through the skeg in line with the slots. Dome head machine screws and nuts are fastened through the slots and the bores of the skeg. These slots allow the skeg protector to yield somewhat on impact with a submerged object.
U.S. Pat. No. 5,277,632, which issued to Davis on Jan. 11, 1994, describes a boat motor replacement skeg. The skeg is thin and flat and has a cavity formed in one of its edges. The replacement skeg is slid over the stub which remains after the original skeg is broken off, and is fastened to the skeg stub with silicone sealant and rivets. As an alternative, the replacement skeg may be part of an original design to replace a specific breakaway skeg having a particular mounting structure.
U.S. Pat. No. 5,772,481, which issued to Alexander et al. on Jun. 30, 1998, discloses a skeg construction for a marine propulsion unit. A skeg assembly for a marine propulsion unit includes a generally U-shaped saddle that is removably attached to the lower torpedo section of the gear case of the propulsion unit and a thin wedge-shaped skeg extends downwardly from the saddle. During planing conditions of the boat, the water line is slightly below the lower torpedo section so that the saddle is out of the water. The side surfaces of the skeg have opposed water intake openings each of which is bordered rearwardly by a laterally projecting shoulder that terminates in a sharp vertical edge and the intake openings are bordered forwardly by a curved surface that connects the side surfaces of the skeg. The water intake openings communicate with a water passage in the skeg which, in turn, communicates with a water passage in the torpedo section so that water can be delivered to the cooling system of the propulsion unit.
U.S. Pat. No. 6,503,110, which issued to Lammli on Jan. 7, 2003, describes a lower unit guard for an outboard motor. It includes a mounting adapter to be secured onto a flange on a housing of a boat motor. The mounting has a leading edge. A skeg receiving pocket is provided which is adapted to receive a skeg of the boat motor. The skeg receiving pocket is adapted to accommodate in close fitting relation the skeg in its entirety. The skeg receiving pocket has a leading edge, a trailing edge, and a bottom edge. A reinforcement member is adapted to fit the contours of a lower unit of a boat motor. The reinforcement member has an upper extremity secured to the leading edge of the mounting and a lower extremity secured to the leading edge of the skeg receiving pocket.
U.S. Pat. No. 6,966,806, which issued to Bruestle et al. on Nov. 22, 2005, discloses a replaceable leading edge for a marine drive unit. A marine propulsion device is made of first and second portions which are removably attachable to each other. The second portion is the leading edge portion of the nose cone and the driveshaft housing. It can also comprise a portion of the skeg. The second portion is configured to crush more easily in response to an impact force from the first portion. This can be accomplished by making the second portion from a different material than the first portion, which can be aluminum, or by providing one or more crush boxes within the structure of the of the second portion to cause it to yield more quickly to an impact force and thus protect the first portion which is the more critical structure of the marine device.
U.S. Pat. No. 7,188,581, which issued to Davis et al. on Mar. 13, 2007, discloses a marine drive with integrated trim tab. The marine drive and the marine vessel are disclosed in which the drive combination has a trim tab with a forward end pivotally mounted to a marine propulsion device.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
The concept of having a breakaway skeg attached to a gear case of a marine propulsion device is very well known to those skilled in the art. As described above, breakaway and replacement skegs of many different types and designs are known. However, in recent years, marine propulsion devices have been developed in which it has become advantageous to be able to more precisely determine the force and resulting moment that is necessary to cause a skeg to be detached from its associated gear case. Breakaway skegs have always been intended to avoid more serious damage to the marine propulsion drive unit. The purpose of a breakaway skeg is to allow it to be sacrificed before damage can occur to the marine drive unit. However, certain types of marine propulsion devices can benefit significantly if the moment necessary to separate the skeg can be more accurately predetermined. It would therefore be significantly beneficial if a breakaway skeg could be provided which allows the accurate predetermination of the breakaway moment.